Some subsea oil and/or gas wells have a type of horizontal Christmas tree (HXT) installed (about 500+ units on the Norwegian continental shelf). Such HXTs were intentionally built without valves in the vertical bore, and the tubing with hanger was lowered through the pre-installed HXT on the subsea template. The reason for this was low need for maintenance. However, the design is was not intended for regular intervention work in the expected lifetime.
Completion integrity issues, production decrease and subsea well slot shortage demanded re-use of slots with new completion much earlier than anticipated. This, together with better drilling and completion technology made it economical viable to continue to develop a subsea field more like a conventional platform dry X-tree field.
To do this type of completion workover operations there is a need to transfer the well from production mode into drilling mode (i.e. to kill the well) in a safe manner. There has been a development in equipment and methods to do this in a most suitable way.
With RLWI (Riserless Light Well Intervention) operations are performed by means of a smaller dynamic positioned vessel and a purpose build subsea well control stack with wireline BOP. This operation needs to be done before the drilling rig arrives. It includes connection and testing of subsea stack, removing the crown plug by wireline, install a lower barrier, a punch circulation hole through the tubing wall and installation of a top barrier below the HXT. Then the RLWI stack must be rigged down and the vessel removed.
Alternatively, a rig with an additionally lower riser package (LRP) including a blowout preventer (BOP) can be used to perform this well intervention operation. The disadvantage with this type of operation is the amount of equipment needed in addition to the standard drilling BOP and LP riser. This type of prior art requires multiple re-connection operations to the subsea installation. Again a wireline crew is needed to retrieve the crown plug and install barrier plugs in the well to secure the well before disconnection of the LRP subsea stack.
In yet an alternative, a standard drilling setup with BOP and LP riser and an in-riser landing string including a top side blowout preventer (wireline BOP) may be used. A lot of extra equipment is needed in addition to the standard drilling BOP and LP riser and also here a wireline crew is needed for retrieving the crown plug.
Consequently, the disadvantages with these types of operations are that they are time consuming, relatively complicated and costly. Moreover, the weather window for performing such operations must be relatively large.
In all of the above operations, the crown plug must be removed before any type of tool can be inserted into the well. The subsea lubricator or the blowout preventer are ensuring well pressure integrity during the removal of the crown plug.
Today, a retrieval tool is used to retrieve the crown plug from the tree before the well operation, and a setting tool is used to set the crown plug in the tree after the operation again. One type of setting and retrieving tool is the Interwell GS running and pulling tool. This tool must be reconfigured between the retrieval and setting of the crown plug.
The crown plug is often referred to as an internal tree cap (ITC) plug. One example of a known crown plug the Aker ITC plug. The Aker ITC plug is illustrated in FIG. 1 in its run state and in FIG. 2 in its set state. It should be noted that FIGS. 1 and 2 are illustrations only—with main focus on the connection interface for setting and/or retrieval tool.
Consequently, the object of the invention is to provide a method for setting and retrieving crown plugs in horizontal subsea trees where costs and complexity are reduced, where well integrity is maintained or even improved and where the time window for the operation is reduced.
Moreover, the object of the invention is to provide a device for setting and retrieving crown plugs in horizontal subsea trees, where the device can run, set, retract, reset and retrieve the crown plug multiple times, without the need to bring the device and crown plug to the surface for reconfiguration.